Javascript timestamp to relative time

Update April 4, 2021:

I've converted the below code to a node package. Here's the repository.

Intl.RelativeTimeFormat - Native API

[✔] (Dec' 18) a Stage 3 proposal, and already implemented in Chrome 71
[✔] (Oct' 20) at Stage 4 (finished), and ready for inclusion in the formal ECMAScript standard

// in miliseconds
var units = {
  year  : 24 * 60 * 60 * 1000 * 365,
  month : 24 * 60 * 60 * 1000 * 365/12,
  day   : 24 * 60 * 60 * 1000,
  hour  : 60 * 60 * 1000,
  minute: 60 * 1000,
  second: 1000
}

var rtf = new Intl.RelativeTimeFormat('en', { numeric: 'auto' })

var getRelativeTime = (d1, d2 = new Date()) => {
  var elapsed = d1 - d2

  // "Math.abs" accounts for both "past" & "future" scenarios
  for (var u in units) 
    if (Math.abs(elapsed) > units[u] || u == 'second') 
      return rtf.format(Math.round(elapsed/units[u]), u)
}

// test-list of dates to compare with current date
[
  '10/20/1984',
  '10/20/2015',
  +new Date() - units.year,
  +new Date() - units.month,
  +new Date() - units.day,
  +new Date() - units.hour,
  +new Date() - units.minute,
  +new Date() + units.minute*2,
  +new Date() + units.day*7,
]
.forEach(d => console.log(   
  new Date(d).toLocaleDateString(),
  new Date(d).toLocaleTimeString(), 
  '(Relative to now) →',
  getRelativeTime(+new Date(d))
))

Intl.RelativeTimeFormat is available by default in V8 v7.1.179 and Chrome 71. As this API becomes more widely available, you’ll find libraries such as Moment.js, Globalize, and date-fns dropping their dependency on hardcoded CLDR databases in favor of the native relative time formatting functionality, thereby improving load-time performance, parse- and compile-time performance, run-time performance, and memory usage.

Here is the exact mimic of twitter time ago without plugins:

function timeSince(timeStamp) {
  var now = new Date(),
    secondsPast = (now.getTime() - timeStamp) / 1000;
  if (secondsPast < 60) {
    return parseInt(secondsPast) + 's';
  }
  if (secondsPast < 3600) {
    return parseInt(secondsPast / 60) + 'm';
  }
  if (secondsPast <= 86400) {
    return parseInt(secondsPast / 3600) + 'h';
  }
  if (secondsPast > 86400) {
    day = timeStamp.getDate();
    month = timeStamp.toDateString().match(/ [a-zA-Z]*/)[0].replace(" ", "");
    year = timeStamp.getFullYear() == now.getFullYear() ? "" : " " + timeStamp.getFullYear();
    return day + " " + month + year;
  }
}

const currentTimeStamp = new Date().getTime();

console.log(timeSince(currentTimeStamp));

Gist https://gist.github.com/timuric/11386129

Fiddle http://jsfiddle.net/qE8Lu/1/

Hope it helps.

Well it's pretty easy if you aren't overly concerned with accuracy. What wrong with the trivial method?

function timeDifference(current, previous) {

    var msPerMinute = 60 * 1000;
    var msPerHour = msPerMinute * 60;
    var msPerDay = msPerHour * 24;
    var msPerMonth = msPerDay * 30;
    var msPerYear = msPerDay * 365;

    var elapsed = current - previous;

    if (elapsed < msPerMinute) {
         return Math.round(elapsed/1000) + ' seconds ago';   
    }

    else if (elapsed < msPerHour) {
         return Math.round(elapsed/msPerMinute) + ' minutes ago';   
    }

    else if (elapsed < msPerDay ) {
         return Math.round(elapsed/msPerHour ) + ' hours ago';   
    }

    else if (elapsed < msPerMonth) {
        return 'approximately ' + Math.round(elapsed/msPerDay) + ' days ago';   
    }

    else if (elapsed < msPerYear) {
        return 'approximately ' + Math.round(elapsed/msPerMonth) + ' months ago';   
    }

    else {
        return 'approximately ' + Math.round(elapsed/msPerYear ) + ' years ago';   
    }
}

Working example here.

You might want to tweak it to handle the singular values better (e.g. 1 day instead of 1 days) if that bothers you.